As a conventionally known rotary fluid machine of the type which is provided with an eccentric rotary piston mechanism including an annular piston which is configured to execute an eccentric rotary motion within an annular cylinder chamber, there is a compressor adapted to compress refrigerant by a volume change in the cylinder chamber associated with the eccentric rotary motion of the annular piston. See, for example, Japanese Patent Publication No. JP H6-288358A. As illustrated in FIG. 16 and FIG. 17 which is a cross sectional view taken along line XVII-XVII of FIG. 16 (hatching omitted), the compressor (100) has a hermetic casing (110) in which to house a compression mechanism (eccentric rotary piston mechanism) (120) and an electric motor (not shown) for driving the compression mechanism (120).
The compression mechanism (120) includes a cylinder (121) having an annular cylinder chamber (C1, C2), and an annular piston (122) disposed in the annular cylinder chamber (C1, C2). The cylinder (121) is made up of an outer cylinder (124) and an inner cylinder (125) which are arranged concentrically with each other and the cylinder chamber (C1, C2) is formed between the outer cylinder (124) and the inner cylinder (125).
The cylinder (121) is firmly fixed to the casing (110). In addition, the annular piston (122) is coupled, through a circular piton base (160), to an eccentric part (133a) of a driving shaft (133) coupled to the electric motor. The annular piston (122) is configured such that it executes an eccentric rotary motion with respect to the center of the driving shaft (133).
The annular piston (122) is so configured as to execute an eccentric rotary motion during which the annular piston (122) substantially comes into contact, at a point of the outer peripheral surface thereof, with the inner peripheral surface of the outer cylinder (124) (here, by such “substantial contact” is meant a state in which, although there is technically created a microscopic gap to such an extent that an oil film is formed, refrigerant leakage in the gap is negligible), while at the same time maintaining a state in which a point of the inner peripheral surface thereof substantially comes into contact, at a position 180 degrees out of phase with that outer peripheral surface point, with the outer peripheral surface of the inner cylinder (125). This results in forming an outer cylinder chamber (C1) and an inner cylinder chamber (C2), respectively, outside the annular piston (122) and inside the annular piston (122).
An outer blade (123A) is disposed outside the annular piston (122). An inner blade (123B) is disposed inside the annular piston (122), the inner blade (123B) lying on an extension of the outer blade (123A). The outer blade (123A) is biased radially inwardly of the annular piston (122) and its inner peripheral end is brought into pressure contact with the outer peripheral surface of the annular piston (122). On the other hand, the inner blade (123B) is biased radially outwardly of the annular piston (122) and its outer peripheral end is brought into pressure contact with the inner peripheral surface of the annular piston (122).
The outer blade (123A) divides the outer cylinder chamber (C1) into two partitions. The inner blade (123B) divides the inner cylinder chamber (C2) into two partitions. More specifically, the outer cylinder chamber (C1) is divided by the outer blade (123A) into a high pressure chamber (first chamber) (C1-Hp) and a low pressure chamber (second chamber) (C1-Lp) and the inner cylinder chamber (C2) is divided by the inner blade (123B) into a high pressure chamber (first chamber) (C2-Hp) and a low pressure chamber (second chamber) (C2-Lp). The outer cylinder (124) is provided, in the vicinity of the outer blade (123A), with a suction opening (141) which fluidly communicates with the outer cylinder chamber (C1) from a suction pipe (114) in the casing (110). In addition, the annular piston (122) is provided, in the vicinity of the suction opening (141), with a through-hole (143) by which the low pressure chamber (C1-Lp) of the outer cylinder chamber (C1) and the low pressure chamber (C2-Lp) of the inner cylinder chamber (C2) are brought into fluid communication with each other. Furthermore, the compression mechanism (120) is provided with a discharge opening (not shown) by which both the high pressure chamber (C1-Hp) of the outer cylinder chamber (C1) and the high pressure chamber (C2-Hp) of the inner cylinder chamber (C2) are brought into fluid communication with a high pressure space (S) in the casing (110).
In addition, in this example, an Oldham mechanism (161) as a rotation preventing mechanism is provided which allows the annular piston (122) to execute only eccentric rotary motion (revolution) while on the other hand preventing the annular piston (122) from rotating.
In the compression mechanism (120), when the annular piston (122) executes an eccentric rotary motion as the driving shaft (133) rotates, the volume of each of the outer and inner cylinder chambers (C1, C2) is alternately repeatedly reduced and expanded. When the volume of the cylinder chamber (C1, C2) increases, a suction process in which refrigerant is drawn into the cylinder chamber (C1, C2) from the suction opening (141) is carried out. On the other hand, when the volume of the cylinder chamber (C1, C2) decreases, a compression process in which refrigerant is compressed in the cylinder chamber (C1, C2) and a discharge process in which refrigerant is discharged from the cylinder chamber (C1, C2) into the high pressure space (S) of the casing (110) through the discharge opening are carried out. This high pressure refrigerant discharged into the high pressure space (S) of the casing (110) flows out to a condenser disposed along the refrigerant circuit by way of a discharge pipe (115) provided in the casing (110).
On the other hand, the aforesaid Japanese Patent Publication No. JP H6-288358A discloses another example which is a partial modification of the configuration of FIG. 17, as shown in FIG. 18. In the compression mechanism (120) of this example, the annular piston (122) is so split at a portion thereof as to be formed into a C-shape and the single blade (123) is passed transversely across the split and comes into contact with both the inner peripheral surface of the outer cylinder (124) and the outer peripheral surface of the inner cylinder (125). The inner peripheral surface of the outer cylinder (124) is formed such that its contact portion with the blade (123) has the same curvature radius as that of the outer peripheral surface of the inner cylinder (125). In addition, an Oldham mechanism (not shown) is provided to permit eccentric rotary motion (revolution) of the annular piston (122) about the inner cylinder (125) but prevent rotation of the annular piston (122). Like the example as shown in FIGS. 16 and 17, processes, such refrigerant suction, refrigerant compression, and refrigerant discharge, are accomplished by the eccentric rotary motion of the annular piston (122).